Caption: Figure 10: Burial curve proposed for the Tegulines Clay and diagenetic mineral sequence
. The mineral sequence
including processes of dissolution, oxidation, and precipitation is detailed in function of depth for the telodiagenesis.
Here, the Silgara Formation is composed mainly of pelitic rocks with thin interlayers of psammitic, semipelitic, meta-basic and metacarbonate rocks, which were affected by a regional metamorphism during the Caledonian orogeny, recognizing a different type of metamorphism as revealed by a progressive mineral sequence
that defined a pattern of metamorphic zonation (biotite [right arrow] andalusite [right arrow] cordierite [right arrow] silimanite) after a metamorphism of Buchan type under low-P and high-T conditions.
The required amounts of silica, alumina and alkali and alkaline- earth cations necessary for zeolite formation probably resulted from volcanic glass and primary igneous fenocrystal dissolution, although the plagioclase alteration reaction in the rock matrix, releasing Ca, could also have been responsible for this According to the defined mineral sequence
, it can be deduced that a change in fluid composition occurred as temperature dropped Zeolite formation in the region studied here began with the highest Si activity in fluid and low Si/Al ratio Na zeolites and ended with the lowest Si activity in fluid and high Si/Al ratio Ca zeolites.